1. Field of the Invention
The present invention relates to a mobile communication system in which data exchange between a base station and a mobile terminal is performed in an asynchronous transfer mode (ATM), and particularly to a base station in a mobile communication system.
2. Description of the Related Art
There have been proposed a variety of mobile communication systems. For example, there have been disclosed examples of mobile communication systems such as in Japanese Patent Application Laid-Open Nos. HEI-9-261725(261725/1987), HEI-10-42337(42337/1998) and HEI-10-145835(145835/1998).
The mobile communication system disclosed in the Japanese Patent Application Laid-Open HEI-9-261725 aims at effectively utilizing a link between a base station and an MSC (Mobile Switching Center), by rejecting those data which have not been normally received by the base station at soft hand-over.
FIG. 5 is a block diagram of a base station in a mobile communication system described in the Japanese Patent Application Laid-Open HEI-9-261725.
The base station transmits and receives wireless communication data via antenna 1 and transmission/receipt distribution circuit 3. Wire circuit receiving circuit 15 receives user data from a wire network, and transmits the received user data to a controlling circuit 23 which performs error check of the user data. User data free of errors are converted into wireless communication data and then transmitted, via encoding circuit 17, modulating circuit 19, transmitting circuit 21, transmission/receipt distribution circuit 3 and the antenna 1. Contrary, from the wireless communication data received via antenna 1, transmission/receipt distribution circuit 3, receiving circuit 5, demodulator circuit 7, decoding circuit 9 and error detecting circuit 11, there is extracted a wireless communication quality information which is then transmitted to the controlling circuit 23. This controlling circuit 23 checks a wireless communication quality based on the wireless communication quality information.
The received data are rejected when the check result of the wireless communication quality is very bad, while the received data are outputted via wire circuit transmitting circuit 13 when the check result of the wireless communication quality is favorable.
Meanwhile, there is adopted an ATM network for connecting a transmitting end side base station and a receiving end side base station.
However, there is a problem in the prior art shown in FIG. 5, as follows.
In the mobile communication system shown in FIG. 5, when a transmitting mobile terminal side base station has failed to normally receive data from a transmitting mobile terminal, the transmitting mobile terminal side base station rejects all of the received data. In this case, the transmitting mobile terminal side base station transmits valid data only, to an accompanying or receiving mobile terminal side base station via MSC (Mobile Switching Center), i.e., via ATM (Asynchronous Transfer Mode) network.
In communication via ATM network, data pattern transmitted from a transmitting mobile terminal side base station may differ from that received by a receiving mobile terminal side base station, due to a cause of delay fluctuation. In the mobile communication systems shown in FIG. 5, there are not provided any countermeasures, causing such a first problem that an output pattern at the time of data transmission from receiving mobile terminal side base station toward a receiving mobile terminal differs from a data transmission pattern at the time of data transmission from a transmitting mobile terminal toward a transmitting mobile terminal side base station, due to a cause of fluctuation in an ATM network.
FIG. 6 shows a data transmission sequence between a receiving mobile terminal side base station and a receiving mobile terminal. In FIG. 6, dotted line arrow Y represents a state in which data are outputted in a normal manner.
However, as represented by a solid line arrow Z in FIG. 6, a certain cell data to be received by a receiving mobile terminal side base station has arrived too early due to a delay fluctuation in the ATM network, resulting in that the data output is hastened by one frame, causing occurrence of transmission interval abnormality.
FIG. 7 is a block diagram of a mobile communication system disclosed in the Japanese Patent Application Laid-Open No. HEI-10-42337.
In this mobile communication system, base stations 111, 112, 11n receive wireless communication data at data receiving means 1111, 1121, 11n1, respectively, extract user data, wireless communication quality informations and wireless communication frame numbers from the wireless communication data, respectively, and convert them into short packets, respectively, at short cell generating means 1112, 1122, 11n2. Further, the base stations 111, 112, 11n multiplex a plurality of short cells by short cell multiplexing means 1113, 1123, 11n3, respectively, map the multiplexed data into ATM cells by ATM cell transmitting means 1114, 1124, 11n4, respectively, and then transmit the data to a mobile communication switching station 10.
This type of mobile communication system also has a problem as follows.
First problem resides in that the quality of wireless communication data received by the base stations are checked by the mobile communication switching station 10 in this mobile communication system, so that wireless communication data are transmitted up to the mobile communication switching station 10 even when some error has occurred in the wireless communication data, resulting in wasteful usage of bands.
In FIG. 8, it is supposed that a base station BS(0) has received error data b(0). Since this b(0) is error data, wasteful data is transmitted between the BS(0) and MSC. Unfortunately, the function for rejecting the data is provided in the MSC side, so that the BS(0) is obliged to transmit the error data b(0) to the MSC, resulting in wasteful usage of bands.
Further, at the time of soft hand-over, there exist a plurality of paths from the mobile terminal to base stations and the mobile communication switching station, causing such a second problem that the aforementioned problem will occur in the plurality of paths.
For example, referring to FIG. 8, it can be seen that there is occurring such a situation that bands are wasted between other BS""s and the MSC similarly to between BS(0) and MSC.
Further, since the short cell multiplexing means 1113, 1123, 11n3 are adopted, even short cells of error data are multiplexed due to the aforementioned first and second problems, resulting in a third problem that multiplexing waiting times of other users are increased.
The aforementioned Japanese Patent Application Laid-Open HEI-10-145835 provides a mobile communication system having a transmission path made into an ATM type, by which uninterrupted hand-over can be realized.
In this mobile communication system, when a mobile terminal has moved from one cell to another cell during communication, the frames including the same data received at asynchronous timings different from each other from both wireless base stations in respective cell areas received by a mobile switching center and identified thereby, there is then selected that data the header information of which has the lowest error rate, and frame exchange is performed at a designated timing. Further, replication of frame to be transmitted to a plurality of wireless base stations is performed, transmission timings are specified based on the header information thereof, and transmission is performed by those timings, to thereby realize uninterrupted hand-over.
However, this mobile communication system has a problem due to delay fluctuation, similarly to the mobile communication system disclosed in the aforementioned Japanese Patent Application Laid-Open HEI-9-261725.
The present invention has been carried out in view of the problems in the prior art as described above, and it is therefore an object of the present invention to provide a base station in a mobile communication system, which enables maintenance of a normal transmission interval of data output, and effective usage of bands.
To achieve the above object, there is provided a base station (BS) in a mobile communication system having a wire network adopting an ATM (asynchronous transfer mode) and an asynchronous transfer mode adaptation layer 2 (ATM Adaptation Layer 2: AAL2) in the wire network based ATM network, comprising: a quality checking part for performing quality check of user data received from a transmitting mobile terminal, and for rejecting those data which have failed in satisfying a predetermined quality; and a CPS (Common Part Sub-layer) packet generating part for generating a CPS packet, by adding a wireless communication quality information, a wireless communication frame number and a valid/invalid identifier to that user data which has satisfied a predetermined quality.
In the base station of the present invention, that data which has not been received in a good receiving state is rejected, and instead of such data, there is inserted an invalid or dummy data shorter than a valid data. As a result, a vacancy is created in the relevant band correspondingly to a difference between the length of a valid data length and the length of an invalid data length. This vacant band can be utilized by another user, thereby improving a utilization efficiency of link.
Further, all of the CPS packets are loaded with wireless communication frame numbers, respectively, and the receiving side base station adjusts output intervals of user data based on the wireless communication frame numbers. Thus, the valid data intervals at a transmitting end side mobile terminal can be normally held at a receiving end side base station or at an ATM adaptation layer 2 terminating device.
Further, existing CODEC""s (COder-DECoder) to be provided within mobile terminals include one which does not output a silent packet in a silent state. As such, in the present invention, there is also inserted an invalid data even if any valid data has not been transmitted when a base station receives a wireless data, and the inserted invalid data is rejected at a receiving end side base station or at an AAL2 terminating device. Thus, the output interval between valid user data at a transmitting mobile terminal can be maintained at the time when a receiving end side base station or an AAL2 terminating device outputs the user data.
The base station of present invention further comprising: a CPS packet receiving part for extracting data for quality check to be used for quality check of the user data; and an intra-base station controlling part for notifying the extracted data for quality check to the quality checking part; wherein the quality checking part preserves the quality check data, and utilizes the data for quality check for quality check of the user data.
In the base station of the present invention, the quality checking part outputs an invalid data generated notice to the CPS packet generating part, when the quality checking part has rejected user data from the transmitting mobile terminal, and the CPS packet generating part receives the invalid data generated notice, generates an invalid data shorter than a valid data, and CPS packetize the wireless communication frame number and the valid/invalid identifier received from the quality checking part as well as the generated invalid data.
In the base station of the present invention there is provided a base station, further comprising: a wireless communication layer terminating part; wherein the CPS packet receiving part performs a sequence check based on a wireless communication frame information loaded in a CPS packet; the CPS packet receiving part outputs user data to the wireless communication layer terminating part synchronously with a transmission timing information received from the wireless communication layer terminating part, concerning valid data of those data free of sequence error; and the CPS packet receiving part rejects those data with which sequence error has occurred and rejects invalid data, upon receiving transmission timing information to be received from the wireless communication layer terminating part.
The base station of present invention, wherein the CPS packet receiving part preserves a wireless communication frame number of user data, during output treatment and rejection treatment when the CPS packet receiving part outputs data to the wireless communication layer terminating part and rejects data, respectively.
The base station of present invention, wherein the CPS packet receiving part outputs no data, when no data to be transmitted exist at the time when the CPS packet receiving part receives transmission timing information from the wireless communication layer terminating part.
And, the base station of present invention, further comprising: a CPS-PDU generating part and an asynchronous transfer mode cell generating part; and wherein the wireless communication layer terminating part detects a void frame, if any, in wireless communication frames, and notifies a void data receipt and a wireless communication frame number to the quality checking part; the quality checking part notifies an invalid data generated notice and a wireless communication frame number, to the CPS packet generating part; the CPS packet generating part having received the invalid data generated notice, generates an invalid data and a valid/invalid identifier settled as xe2x80x9cinvalidxe2x80x9d, and CPS packetizes the generated valid/invalid identifier and the received wireless communication frame number; the CPS-PDU generating part multiplexes the CPS packet into a CPS-PDU; and the ATM cell generating part maps the CPS packet multiplexed into the CPS-PDU, into an ATM cell, and outputs the ATM cell to an ATM network.